KB

AgTech - Precision Agriculture: Lecture 3

Overview

  • Precision Agriculture aims to manage soil variability to improve crop yield and resource use.
  • Key components: soil sensing, grid sampling, EMI/EM38, site-specific management, controlled traffic farming (CTF), variable rate (VR) applications.

Why consider soil variability?

  • Soils vary across the landscape in nutrient and water-holding capacity.
  • Variability leads to differences in crop yield and quality.

How can we measure soil variation?

  • Use gridded soil sampling with a grid; GPS locates sampling sites.
  • Grid sampling is effective but can be costly.

Gridded soil sampling to produce maps

  • Superimpose a grid over an area; sample each cell (GPS-based locations).
  • Creates soil variability maps used for decision making.

Soil Phosphorus (Colwell P)

  • Colwell P ranges indicate phosphorus availability in mg/kg.
  • Categories (example):
  • Sample points feed the Colwell P map used for targeted P management.

Electromagnetic Induction (EMI)

  • EMI sensors measure electromagnetic conductivity (ECa) in the soil.
  • Apparent soil conductivity (ECa) often correlates with:
    • Salinity
    • Texture (clay content)
    • Soil water content
  • EMI surveys provide conductivity maps, not direct soil type maps.

EM38 soil survey

  • EM38 delivers conductivity data over paddocks to map variability.
  • Conductivity values are used to infer soil properties and guide management.

How EMI/EM38 works

  • EMI uses a transmitting coil and a receiving coil.
  • Transmitter emits a primary magnetic field; soil generates a secondary magnetic field detected by the receiver.
  • The measured signal strength is related to soil conductivity (ECa).

How does it work? (concepts)

  • Primary field induces eddy currents in soil.
  • Secondary field is sensed; the strength is proportional to ECa.
  • This relates to ion content (salinity), texture, and moisture.

Applications of the EM38

  • Map soil variability across paddocks.
  • Guide variable irrigation and drainage planning.
  • Salinity monitoring and drainage profiling.
  • Contouring, levelling, and irrigation scheduling.

The Importance of Calibration… Ground Truthing

  • Sensor maps show variability but are not enough alone for maps.
  • Calibrate sensor data to actual soil values via soil sampling.
  • Sensor maps can direct sampling regimes and reduce the number of samples needed.

Example – EM38 used to site C-Probes for Irrigation

  • EM38 data can be used to schedule irrigations based on soil variability.

Where should they site the probe?

  • Surface/furrow irrigation context: placement should consider soil type and plant growth.
  • A map of soil types can aid in site selection and irrigation decisions.

Where should they go in the paddock?

  • Use EM38 to classify areas by soil texture/quality (e.g., heavy, medium, light soils).
  • Example mapping: heavy soil (EM38 ≈ 200 mS/m), light soil (≈ 100 mS/m), medium (≈ 150 mS/m).

Precision Agriculture Application Examples

  • Controlled traffic farming (CTF)
  • Interrow sowing
  • Weed management

Controlled-traffic farming (CTF)

  • CT farming guides all machines to follow the same wheel tracks repeatedly.
  • Requires 2–5 cm positioning accuracy (RTK or PPP).

Why control wheel traffic?

  • First tyre pass causes ~90% of soil compaction.
  • Reduces cumulative soil damage from multiple passes.

Why control wheel traffic? (more context)

  • Wheels drive over 20% (best no-till) to 250% (worst horticulture) of paddock area per year.
  • Reducing traffic helps prevent erosion and consolidate soil structure.

Benefits of CTF

  • Reduces fuel consumption (up to 50\%).
  • Improves traction and minimizes overlap during operations.

Opportunity in wetter conditions

  • Controlled traffic allows machinery operation in wetter conditions without excessive soil damage.

Guidance ~ 2 cm

  • The aim is precise guidance (approx. 2 cm) for traffic lanes.
  • Benefits include erosion protection, better water infiltration, improved establishment and yields.

Guidance is about control

  • Guidance refers to control of traffic and operations, not autonomy.
  • Intelligent systems are still needed to manage decisions.

Variable Rate (VR)

  • Modern machines can adjust input rates across a paddock:
    • Seed sowing rate
    • Growth regulators
    • Fertilisers
    • Herbicides/Pesticides
  • Controlled by VR controllers and decision maps.

Why VR?

  • Save input costs and/or optimise yield.
  • Traditional front-loaded N applications can cause leaching after rainfall or denitrification during waterlogging; not matching season variability.
  • VR helps mitigate dead zones and uneven performance.

VR – how it’s done

  • VR requires knowing when/where to adjust rates.
  • Sensors used include:
    • Proximal NDVI (in-season plant reflectance)
    • Satellite NDVI
    • Yield monitors (historic harvest)
  • Sensor measurements generate variability maps used to set application rates.

Summary video

  • Reference: https://www.youtube.com/watch?v=lz76L7qjxzM

What I want you to know

  • Know some applications of precision agriculture.
  • Understand what the EM38 is and how it works.
  • Understand variable rate and site-specific management.
  • Know how this information can be used by a farmer.

Exam preparation (revision prompts)

  • What are the 3 types of variability?
  • What is a type of sensor used for plant sensing? How does it work?
  • Why is the reflectance signature of different plants important?
  • What can the farmer use this information for?
  • How does measuring soil variability work?
  • What can the data be used for?
  • What are some types of precision livestock (PL) technology?
  • What are the benefits and challenges of the different PL technologies?
  • How does GNSS work?
  • Why are there different types of GNSS?